Originally Posted by 1ciderdog
Why not ask the Allison guy that is on this net?
I've not really heard of this happening but it is possible that the older fluid left a film on the clutch plates that led to reduced friction coefficient and slightly elongated shifts. Could be the new fluid dispersants are cleaning the surfaces and returning the surfaces to the original friction coefficient. This would raise the coefficient and make for harsh shifts until the TCM (Transmission Control Module) changes pressures to get the shift times back into calibration. Note: This is a theory but, if it's correct, the problem should get better soon as the TCM shift schedules "fine tunes" the shifts. It should converge shortly.
Hope this helps.
PS: It could also be air in the system if the fluid was low but I would expect all the shifts to be "soft" and not harsh. Also, I would think if it was air entrainment, upshifts and downshifts would be affected.